1. Field of Invention
The present invention relates to an elimination technique of yellow ring occurring on a white light emitting diode (LED). Particularly, the present invention relates to a method and system for eliminating yellow ring occurring on the white LED having a blue light chip exciting yellow phosphor powders and having a packaging surface enclosing thereon.
2. Related Art
Light emitting diodes (LEDs) have been widely used in many applications, such as general lightening, traffic light and displays, due to its low cost, high illumination and energy saving characteristics. Many attentions are drawn that, after white LEDs are developed successfully, human life have been largely promoted and facilitated.
Traditionally, a LED is presented by employing the policy of a mixture of light emitting from a red, green and blue light chip, a blue light chip exciting red and green phosphor powders, and a blue chip exciting yellow phosphor powders, respectively. Among them, the structure of using a blue light chip and yellow phosphor is the most attractive one owing to its simple and cost saving.
However, a yellow ring phenomenon of the lightspots has been generally observed around the kind of white LED having a blue light chip exciting yellow phosphor powders. It is presented because the yellow phosphor powders are not properly dispensed on a uniform arrangement within the packaging surface. In this regard, solutions for such elimination of such yellow ring phenomenon have been proposed hotly.
One solution disclosed a LED packaging structure, in which a phosphor layer is provided for a white light with the phosphor powders contained therein arranged in a particular pattern for reduction of the yellow ring phenomenon. Another solution taught a LED optical lens, where a lens body is provided to have a particular design so that uniformity of the LED illumination arrangement and angle is improved. And another solution suggested a LED packaging structure capable of wide angle and uniform outputting light, in such a manner that the light attenuation issue and secondary packaging issue may be improved and eliminated, respectively.
Also, another prior technology taught a LED based lamp, in which a lens and microlenses each being in a polygonal shape are provided so that the emitted light may be directed to the microlenses through the lens to achieve good light scattering effect. Another solution suggested a LED assembly, where a filter layer is provided to let the LED light with a particular wavelength at least partially reflected, to reduce the yellow ring phenomenon. Another prior art disclosed a LED having at least a porous ceramic element for light scattering. And still other solution proposed a LED with a phosphor coating, in which a dye compound is contained to improve the uniformity of the light distribution pattern viewed externally to the device.
All the prior arts discussed in the above are each presented with a secondary optical element, which has been observed with some shortcomings. For example, the cost for the whole LED structure for elimination of the yellow ring phenomenon may be not low enough, the applicability to all kinds of white LED products is impossible, and the secondary optical elements may have the chance of failure in the real use.
In view of the above discussed issues encountered in the prior art, the inventor of this application suggests a method and system for eliminating yellow ring occurring on the white LED having a blue light chip exciting yellow phosphor powders and having a packaging surface enclosing thereon on a lightspot by lightspot basis, which is performed at a place other than within the packaging surface.